There are a variety of types of magnetic field sensing elements, including, but not limited to, Hall Effect elements, magnetoresistance elements, and magnetotransistors. Different types of Hall Effect elements include planar Hall elements, vertical Hall elements, and circular Hall elements. There are also different types of magnetoresistance elements including, for example, anisotropic magnetoresistance (AMR) elements, giant magnetoresistance (GMR) elements, tunneling magnetoresistance (TMR) elements, Indium antimonide (InSb) elements, and magnetic tunnel junction (MTJ) elements.
Hall effect elements generate an output voltage proportional to a magnetic field. In contrast, magnetoresistance elements change resistance in proportion to a magnetic field. In a circuit, an electrical current can be directed through the magnetoresistance element, thereby generating a voltage output signal proportional to the magnetic field.
Magnetic field sensors, which use magnetic field sensing elements, are used in a variety of applications, including, but not limited to, current sensors that sense magnetic fields generated by currents in a conductor, magnetic switches, proximity detectors that sense the proximity of ferromagnetic or magnetic objects, rotation detectors that sense passing ferromagnetic articles such as gear teeth, and magnetic field density sensors.
Hall Effect elements exhibit an undesirable DC offset voltage. Techniques have been developed to reduce the DC offset voltage, while still allowing the Hall Effect element to sense a DC magnetic field. One such technique is commonly referred to as “chopping” or “current spinning” and entails driving a Hall Effect element in two or more different directions and receiving output signals at different output terminals as the Hall Effect element is differently driven. In this way, selected drive and signal contact pairs are interchanged during each phase of the chopping and offset voltages of the different driving arrangements tend to cancel toward zero.
Chopping is also applied to amplifiers to reduce an offset component and low frequency noise (i.e., flicker noise) of signals applied to the amplifier. Amplifiers implementing chopping are often referred to as chopper-stabilized amplifiers.
Chopping tends to generate undesirable spectral components (i.e., frequency components) and ripple in the resulting signal, which can be removed with filters. While conventional arrangements that use filters can effectively reduce the ripple, it will be understood that the filters tend to reduce a bandwidth or a response time of the magnetic field sensor.
Some applications require circuits to perform self-tests. For example, to adhere to automotive safety standards, circuits may be required to test themselves periodically and/or during operating to ensure the circuits are operating correctly. Processing a test signal may increase bandwidth requirements of certain circuits. It may be desirable for a circuit, such as a magnetic field sensor, to process a test signal while it also processes a signal representing the sensed magnetic field. However, processing multiple signals with different frequency components may require circuit components with greater bandwidth. For example, an amplifier that processes a test signal as well as other signals may require greater bandwidth or risk saturation. This can increase cost and area.